Interferons are proteins having a variety of biological actions including antiviral, immunomodulating and antiproliferative effects. Cellular production of interferons may be stimulated by numerous agents, including viruses. Interferons protect animal tissues and cells against viral attack and are an important host defense mechanism. Interferon may be produced endogenously by numerous cell types such as leukocytes, fibroblasts and lymphocytes, and may also be produced in cell culture or recombinantly. In most cases, interferons provide better protection to tissues and cells of the kind from which they have been produced than to other types of tissues and cells, indicating that human-derived interferon should be more efficacious in treating human diseases than interferons from other species. There are several distinct types of interferons, generally classified as alpha, beta, gamma and omega interferons, and a large number of variants thereof.
The alpha and omega interferons are derived primarily from leukocytes. Cell-derived interferon such as leukocyte interferon is difficult to purify to homogeneity and, as a consequence, is most often used as a crude or partially purified preparation. Leukocyte interferon preparations contain two molecular populations (alpha and omega interferons) that are distinguishable physically, chemically and biologically. Alpha interferon comprises approximately 80% of leukocyte interferon activity, and omega interferon comprises about 20% of leukocyte interferon activity. The leukocyte interferon forms can be separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) into slow- and fast-migrating components as described by Stewart II, W. E. and Desmyter, J. ViroIogy 67:68-73 (1975). The larger leukocyte interferon forms have apparent molecular weights of about 21,000-25,000 Daltons, while the smaller leukocyte interferon forms have apparent molecular weights of about 15,000-18,000 Daltons. The larger (omega) interferon are glycosylated, whereas the smaller (alpha) interferon are not. General discussions of these and other interferons can be found in various texts and monographs including: The Interferon System by W. E. Stewart, II, Springer-Verlag, New York (1979); and Interferon Therapy, World Health Organization Technical Reports Series 676, World Health Organization, Geneva (1982).
The method of administering interferon is an important factor in the clinical application of this important therapeutic agent. Systemic administration of interferon by either intravenous, intramuscular or subcutaneous injection has been most frequently used with some success in treating disorders such as hairy cell leukemia and Acquired Immune Deficiency Syndrome (AIDS)--related Kaposi's sarcoma. Among the problems inherent in intravenous, intramuscular or subcutaneous administration is that interferon can come into contact with uninfected or nonmalignant cells, and may thereby cause unwanted side effects such as fever, malaise and myalgia.
In some cases it would be preferable to administer interferon directly to the affected tissues or organs. This may be accomplished by direct injection of interferon into the diseased site such as done in selected cases of condylomata acuminata (genital warts), involving the external surfaces of genital or perianal areas. Interferon can also be administered by local topical application directly to the diseased site, such as a viral-induced skin lesion. Topical interferon may be useful for treatment of conditions such as condylomata acuminata, cervical dysplasia, rectal cancer, basal cell carcinoma, penile cancer or any other disorder responsive to interferon, particularly those linked to papilloma virus infection. Topical application in these cases could reduce the unwanted side effects associated with intramuscular, intravenous or subcutaneous administration. Also, the patient could self-administer topical interferon without the direct assistance of a qualified health-care worker. A topical interferon product could also promote patient compliance by providing a more pleasant therapeutic experience for the patient than interferon treatment via injection.
The lack of interferon stability in solutions and other products has heretofore limited its utility. Interferon products having enhanced storage stability should facilitate more wide-spread use of this important therapeutic agent. Several factors are important in designing a useful topical interferon preparation. First, conventional topical interferon preparations are generally considered unstable, and therefore are considered to have a limited shelf-life. A topical interferon preparation should be stabilized to prevent degradation over time and upon shipping and handling. Second, because interferon generally has a higher molecular weight than the molecular weights of the therapeutic agents usually administered in topical preparations, interferon should be incorporated into a substance which sufficiently holds the high molecular weight interferon in suspension during packaging, shipping and application, and yet also be able to release the substance from the preparation in a reasonable length of time once it has been applied to the diseased site. Third, the preparation must not adversely affect the antiviral activity of interferon.
The present invention describes new, improved stabilizers and methods for stabilizing interferon, meeting the requirements for topical interferon products defined above and for stabilized interferon solutions.
Other interferon-stabilizing agents have been described and used to stabilize interferon.
Estis et al. in U.S. Pat. No. 4,680,175 describe the use of protease inhibitors such as alpha-1-antitrypsin inhibitor, alpha-2 macroglobulin, soybean inhibitor, N-alpha-tosyl-L-lysine chloromethyl ketone, phenylmethylsulfonyl fluoride, and N-alphatosylphenylalanine chloromethyl ketone to stabilize topical interferon preparations. Miller, in U.S. Pat. No. 4,957,734, discloses the use of anionic, cationic and nonionic surface active agents but claims no stabilization of interferon. Miller discloses that quarternary ammonium detergents such as cetyl pyridinium chloride and benzalkonium chloride are preferable cationic agents. Hasegawa et al. in U.S. Pat. No. 4,675,184 teach that anionic surface active agents such as sodium alkyl sulfates stabilize betainterferon (fibroblast-derived) but only in conjunction with a polyhydric sugar alcohol and an organic buffer as stabilizers.
Stewart et al. in U.S. Pat. No. 3,981,991 teach that interferon can be stabilized by treating the antiviral agent with a combination of: 1) guanidine-hydrochloride or urea; 2) mercaptoethanol or ethanethiol; and 3) an agent selected from the group consisting of sodium dodecylsulfate, sodium decylsulfate, sodium dodecylsulfonate, dodecylamine and decylamine. Stewart et al. caution that interferon cannot be stabilized with only one or two of the aforesaid three agents.
None of these patents teach that human alpha and omega interferons or mixtures thereof can be stabilized with only the stabilizing agents described herein.